1. Field of the Invention
The present invention relates to a liquid discharging substrate, a printhead, and a printing apparatus.
2. Description of the Related Art
A printing apparatus includes a printhead. For example, in an inkjet printing apparatus, a plurality of nozzles for discharging ink (printing material) are provided in the printhead. Japanese Patent Laid-Open No. 2005-104142 exemplifies a printhead substrate including a discharging unit, or a printing unit, corresponding to each nozzle, a signal generating unit that generates a signal based on printing data, and a level shifter that shifts the level of the generated signal and outputs the signal to the discharging unit.
The discharging unit includes, for example, a printing element (for example, electrothermal transducer), and a switching element (for example, transistor) that is connected to the printing element and is turned on in response to a signal from the level shifter. The discharging unit is driven by controlling the switching element and supplying a current to the printing element. When the discharging unit is driven, noise may be generated on the power supply line of the level shifter owing to the control of the switching element.
The signal generating unit receives, for example, a voltage (for example, 3.3 to 5 [V]) for a logic circuit. The level shifter receives, for example, a voltage (for example, 12 [V]) that is larger in voltage value than the voltage for the logic circuit and is used to shift the level of a signal from the signal generating unit. Both the signal generating unit and the level shifter receive, for example, a common ground voltage (0 [V]).
In this arrangement, noise of the ground voltage generated in the level shifter at the time of driving the discharging unit propagates to the signal generating unit through a wiring line for supplying the ground voltage, and may cause the malfunction of the signal generating unit. When the number of discharging units (the number of nozzles) is increased, the number of switching elements is also increased, so the noise becomes a serious problem. Note that Japanese Patent Laid-Open No. 2005-104142 does not consider this noise.